Method and apparatus for handling random access channel responses

ABSTRACT

A method and apparatus for supporting a random access using a random access channel (RACH) are disclosed. The WTRU detects a format of control information in at least one control channel element (CCE) of a common area in a control portion of a downlink transmission. The control information indicates a resource allocation in a data portion of the downlink transmission. The WTRU recovers a random access response assigned to the WTRU from the indicated resource allocation of the data portion on a condition that the at least one CCE has a random access radio network terminal identifier (RA-RNTI) assigned to the WTRU.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.12/260,495 filed Oct. 29, 2008 and claims the benefit of U.S.provisional application No. 60/983,473 filed on Oct. 29, 2007, theentire contents which are incorporated by reference as if fully setforth.

FIELD OF INVENTION

The present application is related to wireless communications.

BACKGROUND

The objective of evolved universal terrestrial radio access (E-UTRA) andlong term evolution (LTE) in wireless communications is to develop aradio access network towards a high-data-rate, low-latency,packet-optimized system with improved system capacity and coverage. Inorder to achieve these goals, an evolution of the radio interface aswell as the radio network architecture is being considered. For example,orthogonal frequency division multiple access (OFDMA) and frequencydivision multiple access (FDMA) are proposed air interface technologiesto be used in the downlink and uplink transmissions, respectively,instead of using code division multiple access (CDMA), which iscurrently used in 3rd Generation Partnership Project (3GPP)communication systems. Another change includes applying all packetswitched service, which means all the voice calls will be made on thepacket switched basis.

Packet switched communications operate on a random access channel. Thephysical channel specification for LTE specifies that the random accessburst occupies a bandwidth corresponding to 72 sub-carriers (6 resourceblocks). The set of six resource blocks is referred to as onetime-frequency random access resource, or alternatively, resources ofone LTE physical random access channel (PRACH). For the systemflexibility, having a configurable number of time-frequency randomaccess resources in one radio frame (10 ms) depends on the systembandwidth and the random access load. The existence of any additionallyconfigured time-frequency random access resources needs to be explicitlysignaled to wireless transmit/receive units (WTRUs).

There may be multiple random access preambles that are available for theaccess in one time-frequency random access resource, and the number ofrandom accesses that expect the responses in a certain time window mayvary greatly. If an evolved Node-B (eNB) always needs to signal allresponses in one transport block per one random access-radio networktemporary identity (RA-RNTI), the resultant size of the transport blockmay reduce the scheduling flexibility of the random access response.

SUMMARY

A method and apparatus for supporting a random access using a randomaccess channel (RACH) are disclosed. Each of a plurality of wirelesstransmit/receive units (WTRUs) sends a random access request to a basestation on an uplink RACH preamble. A RACH Response, sent by the basestation, is received by each WTRU. A control signal portion of the RACHResponse indicates the location of the RACH Response message in acorresponding data portion. The RACH Response control information isdefined by single or multiple control channel elements (CCE), where eachWTRU is allocated at least one CCE to provide its unique RACH Responsecontrol signal. The WTRU is configured to locate its intended CCE fromamong the multiple CCEs sent by the base station.

BRIEF DESCRIPTION OF THE DRAWINGS

A more detailed understanding may be had from the following description,given by way of example in conjunction with the accompanying drawingswherein:

FIG. 1 shows a wireless communication network using random access;

FIG. 2 shows a format for a RACH Response control channel and datachannel;

FIG. 3 shows an alternative format for a RACH Response control channel;and

FIG. 4 shows a WTRU configuration for receiving a RACH Response.

DETAILED DESCRIPTION

When referred to hereafter, the terminology “wireless transmit/receiveunit (WTRU)” includes but is not limited to a user equipment (UE), amobile station, a fixed or mobile subscriber unit, a pager, a cellulartelephone, a personal digital assistant (PDA), a computer, or any othertype of user device capable of operating in a wireless environment. Whenreferred to hereafter, the terminology “base station” includes but isnot limited to a Node-B, a site controller, an access point (AP), or anyother type of interfacing device capable of operating in a wirelessenvironment.

Herein, the term “RACH Response” is used interchangeably with an accessindication channel (AICH) message.

FIG. 1 shows a wireless communication network 100, in which a basestation 101 grants random access to a plurality of wirelesstransmit/receive units (WTRUs) 102-104. A RACH Response signal 105 issent to the WTRUs 102-104 granting random access resource allocations inresponse to random access requests 106-108 sent by the WTRUs 102-104.The random access requests 106-108 are sent in RACH preambles from thesame random access burst. A single time-frequency random access resourceis granted per random access request by one of the WTRUs 102-104.Alternatively, multiple time-frequency random access resources may begranted per random access request.

FIG. 2 shows a RACH Response format 201 comprising a control channel 202and a data channel 203 according to a first embodiment. By way ofexample, the control channel 202 may be a physical downlink controlchannel (PDCCH) and the data channel 212 may be a physical downlinkshared channel (PDSCH). The control channel 202 includes a commoncontrol portion 203, in which a plurality of control channel elements(CCEs), CCE-0 to CCE-N, are defined for RACH Responses intended forWTRUs 102-104. Each set of CCEs contains location information fordirecting each respective WTRU to the RACH Response resource allocationfound on the data channel 212 in transport blocks TB-0 to TB-N.

The CCEs may also include transport format information, such as thetransport formats and modulation and coding scheme (MCS) to be used fordecoding the RACH Response message on the data channel 203.

In the first embodiment, the WTRUs 102-104 perform blind decoding of thecommon control elements CCE-0 to CCE-N within the common control portion203, searching for their respective CCE having the intended RACHResponse control information. The starting location of the commoncontrol signal portion 203 may be pre-defined. For example, the startinglocation may be set to CCE-0, as shown in FIG. 2. The required RACHResponse resources (i.e., the number of common control elements) mayvary based on the number of WTRUs requiring the random access responses.A maximum number of CCEs may be specified accordingly.

FIG. 3 shows an alternative embodiment to the starting point beingdefined as CCE-0, where a subset L of CCEs between CCE-N and CCE-M maybe allocated for a RACH Response common control portion 303. Forexample, CCE-N to CCE-N+L may be allocated for the common controlportion 303, as shown in FIG. 3. Alternatively, the common controlportion 303 may be allocated to CCE-M-L to CCE-M, or any other subset ofCCEs.

The starting location of the RACH Response common control portion 303,the number of CCEs, and/or the subset of L CCEs may be received by theWTRUs 102-104 in one of the broadcast channel (BCH) system informationblocks (SIBs).

FIG. 4 shows a WTRU 401 configured to receive and process the RACHResponse 105 from a base station 411. At the base station 411, a cyclicredundancy code (CRC) generator 414 computes a CRC which is added as aset of bits onto CCE control information 420. The CRC is first is maskedby an ID code at mask encoder 413. The masked CRC is then added to theCCE information 420. As an example, a 16-bit CRC code may be masked by a16-bit ID, and then encoded onto the control information 420 fortransmission at transmitter 412.

At WTRU 401, receiver 402 demodulates the received RF RACH Responsesignal 105, and blind decoder 403 processes the demodulated receivedsignal 105, for example, by using a forward error correction (FEC) codeor a Viterbi code. A CRC de-masker 404 processes the CRC bits byde-masking them according to the ID code. Next, a CRC decoder 405decodes the de-masked CRC bits, allowing the WTRU 401 to perform anerror check on the received CCEs of the RACH Response. The blind decoder403, CRC de-masker 404, and CRC decoder 405 may be implemented as asingle processor or as separate individual processors.

The ID code may be a Group ID or a WTRU-specific ID. The Group ID isused when a set of WTRUs served by the base station 411 are to receive acommon RACH Response. The ID code may be a temporary ID assigned to aWTRU to identify the RACH Response addressed to it even if sharing aGroup ID with other WTRUs. For example, the temporary ID may be a RACHradio network temporary ID (RA-RNTI). The ID code is received by theWTRU 401 with other system parameters when it initially acquires a celland camps on the cell of the base station 411 via higher layersignaling.

Alternatively, a fixed time-frequency resource allocation may bededicated to the CCEs corresponding to the random access grant controlin the RACH Response. This fixed resource allocation may be independentof the other physical channel allocations, such as a physical HARQindicator channel (PHICH) location, and avoids the need to have anyknowledge of the configuration of those other physical channels. Forexample, the fixed time-frequency resource allocation dedicated to theRACH Response control may be allocated at a location immediatelyfollowing a particular type of physical channel, such as a physicalcontrol format indicator channel (PCFICH).

For better performance and scheduling flexibility, the CCEs may bespread in time-frequency domain, within the control portion of asub-frame. A one-to-one association (e.g., a time offset) between therandom access request in the RACH preamble and a dedicatedtime-frequency resource allocation may be used to provide WTRU-specificRACH Response control.

In a second embodiment, multiple RACH Responses are sent to each ofseveral different WTRUs. In a first alternative, each RACH Responsecontrol portion only contains resource allocation and transport formatinformation for one WTRU RACH Response data portion. In anotheralternative, each RACH Response combines both control and data portionstogether for one WTRU. The RA-RNTI may be used to scramble each RACHResponse control portion or the combined RACH Response control and data.Optionally, the RA-RNTI may be used to scramble the RACH Response dataportion since a WTRU knows that the RACH Response data portion part isintended for it based on the RACH Response control portion.

Different antenna configurations may be applied to different RACHresponses based on different WTRUs' capabilities. For examplemultiple-input multiple-output (MIMO) or space frequency block coding(SFBC) may be applied based on the WTRUs' capabilities.

For both alternatives, the first RACH Response data portion or RACHResponse control portion may contain the information of how many totalRACH Response data portions or RACH Response control portions are to besent for different WTRUs. From this, the WTRUs know how many RACHResponses they need to detect to find the specific RACH Responseintended to them. In doing this, the WTRUs associated with one RA-RNTIdo not need to monitor all RACH Response channels, thus reducing thedetection complexity and saving power.

If frequency hopping is employed for the RACH Response, the frequencyhopping pattern for transmission of the RACH Response control or dataportions may be indicated in the first RACH Response control portion orthe combined RACH Response data and control. The transport format (suchas MCS or power for different WTRUs) may vary for RACH Response dataportion which is signaled in the RACH Response control portion. Whencombining the RACH Response control and data parts together, there is noneed to signal the resource allocation for the RACH Response dataportion.

The location of the RACH Response per WTRU may be fixed or spread acrossthe time-frequency spectrum. It may be standardized or signaled in oneof the BCH SIBs.

For the first and the second embodiments for the RACH Response, thenetwork may decide which format should be used for the RACH Response.The exact RACH Response to be used may be signaled in the BCH so thatthe WTRU knows how to perform the blind decoding. For example, the WTRUmay receive a downlink control indicator (DCI) format code, detected bythe blind decoder 403, from which the WTRU may know the size (e.g.,number of CCEs) of the RACH Response control portion and/or the startinglocation of the RACH Response control on the sub-frame.

Different RACH Response locations for different WTRUs may be associatedwith WTRU IDs (e.g., cell radio network temporary identity (C-RNTI),international mobile subscriber identity (IMSI), international mobileequipment identity (IMEI), or any other WTRU ID). The WTRU IDs may beknown from the paging information. The relation between the WTRU ID andits RACH location may be pre-defined. In this way, the WTRU knows whereto look for its RACH channel.

As an alternative, the initial RACH response location for the WTRU maybe signaled in the BCH or derived from a relation between the WTRU IDand RACH location and then the WTRU may get the location of subsequentRACHs in the first RACH Response message signaled, (e.g., in case thatthe WTRU fails at the first RACH and has to send another RACH).

It should be noted that although the embodiments are described withreference to LTE, this is an example implementation, and the embodimentsmay be applied to any other wireless communication systems, such as highspeed packet access (HSPA) systems or future development, and otherwireless system when similar services and concepts are supported.

Although features and elements are described above in particularcombinations, each feature or element can be used alone without theother features and elements or in various combinations with or withoutother features and elements. The methods or flow charts provided hereinmay be implemented in a computer program, software, or firmwareincorporated in a computer-readable storage medium for execution by ageneral purpose computer or a processor. Examples of computer-readablestorage mediums include a read only memory (ROM), a random access memory(RAM), a register, cache memory, semiconductor memory devices, magneticmedia such as internal hard disks and removable disks, magneto-opticalmedia, and optical media such as CD-ROM disks, and digital versatiledisks (DVDs).

Suitable processors include, by way of example, a general purposeprocessor, a special purpose processor, a conventional processor, adigital signal processor (DSP), a plurality of microprocessors, one ormore microprocessors in association with a DSP core, a controller, amicrocontroller, Application Specific Integrated Circuits (ASICs), FieldProgrammable Gate Arrays (FPGAs) circuits, any other type of integratedcircuit (IC), and/or a state machine.

A processor in association with software may be used to implement aradio frequency transceiver for use in a wireless transmit receive unit(WTRU), user equipment (UE), terminal, base station, radio networkcontroller (RNC), or any host computer. The WTRU may be used inconjunction with modules, implemented in hardware and/or software, suchas a camera, a video camera module, a videophone, a speakerphone, avibration device, a speaker, a microphone, a television transceiver, ahands free headset, a keyboard, a Bluetooth® module, a frequencymodulated (FM) radio unit, a liquid crystal display (LCD) display unit,an organic light-emitting diode (OLED) display unit, a digital musicplayer, a media player, a video game player module, an Internet browser,and/or any wireless local area network (WLAN) or Ultra Wide Band (UWB)module.

What is claimed is:
 1. A wireless transmit/receive unit (WTRU),comprising: a processor configured to: transmit a random accesspreamble; receive a control channel of a downlink transmission, whereina common control portion of the control channel of the downlinktransmission comprises a number of control channel elements (CCEs), andwherein the number of CCEs comprises control information for one or morerandom access responses; perform blind decoding within the CCEs of thecommon control portion of the control channel of the downlinktransmission to detect control information intended for the WTRU,wherein the control information comprises a resource allocation to beused for receiving a random access response in a data portion of thedownlink transmission; and process the random access response in thedata portion of the downlink transmission in accordance with theresource allocation decoded in the common control portion of the controlchannel of the downlink transmission.
 2. The WTRU of claim 1, whereinthe blind decoding is performed using a random access radio networktemporary identifier (RA-RNTI) assigned to the WTRU.
 3. The WTRU ofclaim 2, wherein a cyclic redundancy check (CRC) is masked with theRA-RNTI.
 4. The WTRU of claim 2, wherein the RA-RNTI is utilized by aplurality of WTRUs.
 5. The WTRU of claim 1, wherein the control channelincludes a physical downlink control channel (PDCCH), and wherein thedata portion includes a physical downlink shared channel (PDSCH).
 6. TheWTRU of claim 1, wherein a maximum number of CCEs in the common controlportion of the control channel of the downlink transmission isspecified.
 7. The WTRU of claim 1, wherein a starting CCE in the commoncontrol portion of the control channel of the downlink transmissioncorresponds to a first CCE in the control channel of the downlinktransmission.
 8. The WTRU of claim 1, wherein the number of CCEs in thecommon control portion of the control channel of the downlinktransmission corresponds to a number of consecutive CCEs in the controlchannel of the downlink transmission.
 9. The WTRU of claim 1, whereinthe common control portion of the control channel of the downlinktransmission comprises control information for a random access responseintended for at least one other WTRU.
 10. The WTRU of claim 1, whereinthe control channel comprises a total number of CCEs, and the number ofCCEs in the common control portion is a subset of the total number ofCCEs of the control channel.
 11. A method performed by a wirelesstransmit/receive unit (WTRU), the method comprising: transmitting arandom access preamble; receiving a control channel of a downlinktransmission, wherein a common control portion of the control channel ofthe downlink transmission comprises a number of control channel elements(CCEs), and wherein the number of CCEs comprises control information forone or more random access responses; performing blind decoding withinthe CCEs of the common control portion of the control channel of thedownlink transmission to detect control information intended for theWTRU, wherein the control information comprises a resource allocation tobe used for receiving a random access response in a data portion of thedownlink transmission; and processing the random access response in thedata portion of the downlink transmission in accordance with theresource allocation decoded in the common control portion of the controlchannel of the downlink transmission.
 12. The method of claim 11,wherein the blind decoding is performed using a random access radionetwork temporary identifier (RA-RNTI) assigned to the WTRU.
 13. Themethod of claim 12, wherein a cyclic redundancy check (CRC) is maskedwith the RA-RNTI.
 14. The method of claim 11, wherein the controlchannel includes a physical downlink control channel (PDCCH), and thedata portion includes a physical downlink shared channel (PDSCH). 15.The method of claim 12, wherein the RA-RNTI is utilized by a pluralityof WTRUs.
 16. The method of claim 11, wherein a maximum number of CCEsin the common control portion of the control channel of the downlinktransmission is specified.
 17. The method of claim 11, wherein astarting CCE in the common control portion of the control channel of thedownlink transmission corresponds to a first CCE in the control channelof the downlink transmission.
 18. The method of claim 11, wherein thenumber of CCEs in the common control portion of the control channel ofthe downlink transmission corresponds to a number of consecutive CCEs inthe control channel of the downlink transmission.
 19. The method ofclaim 11, wherein the common control portion of the control channel ofthe downlink transmission comprises control information for a randomaccess response intended for at least one other WTRU.
 20. The method ofclaim 11, wherein the control channel comprises a total number of CCEs,and the number of CCEs in the common control portion is a subset of thetotal number of CCEs of the control channel.